This invention relates to imaging equipment and, more particularly, to a device and method for scanning using an illumination source with an inverted radiation profile.
Optical scanners generate machine-readable image data representative of a scanned object such as an image on a paper document or other media having an image or other data thereon to be scanned. Flatbed optical scanners are stationary devices which have a transparent, platen upon which the object to be scanned is placed. Equipment such as flat bed scanners, film scanners, copiers, multi-function devices and some digital cameras may use a linear cold cathode fluorescent lamp (CCFL) as the light source. The object is scanned by sequentially imaging narrow strips or scan line portions of the object by an imaging apparatus such as a charge-coupled device (CCD). The imaging apparatus produces image data which is representative of each scan line portion of the scanned object. A linear arrangement of light sensitive elements, such as CCD photodetectors, is used to convert light into electric charges. There are many relatively low-priced color and black and white, one-dimensional array CCD photodetectors available for image scanning systems. Electronic imaging systems may alternatively use two-dimensional arrays of light sensitive elements such as CCD arrays.
While linear CCFLs are bright, inexpensive, and reliable, they also have one major disadvantagexe2x80x94they have a non-uniform illumination intensity profile that requires corrective analog or digital gain to normalize. Scanner systems employing these devices suffer from low signal-to-noise ratios at the ends of the scan lines due to decreased light intensity on the page and through the optical system.
In accordance with an embodiment of the present invention, an imaging device comprising a linear illumination source having two ends and operable to radiate light on a scan object, the illumination source radiating light along a length hereof, the light radiated from the illumination source having a minimum intensity at a midpoint thereof and at least one conversion element operable to convert light into electric charges corresponding to an image, is provided.
In accordance with another object of the present invention, a method for imaging a scan object comprising radiating light from a linear illumination source having two endpoints onto the scan object, the light radiated from the illumination source having a maximum intensity at the two endpoints of the illumination source and a minimum intensity at a midpoint of the illumination source is provided.